1. Field of the Invention
The present invention generally relates to a throttle body for controlling a suction air quantity flowing in a suction passage. More specifically, a first aspect of the present invention relates to an improvement in shape of a throttle valve to be provided in the throttle body. A second aspect of the present invention relates to an improvement in structure of the throttle body for restricting a rotative angle of the throttle valve to be operated by a motor. A third aspect of the present invention relates to an improvement in drainage structure for the motor, in the throttle body. Finally, a fourth aspect of the present invention relates to an improvement in mount structure of a throttle shaft for rotatably mounting the throttle valve.
2. Related Art
In relation to the first aspect of the present invention, a known throttle valve has a shape substantially corresponding to a sectional shape of a suction passage. However, such a throttle valve has a problem that there occurs scuffing or biting with respect to an inner wall of the suction passage in the vicinity of a throttle shaft. Japanese Utility Model Laid-Open Publication No. 61-137858 has proposed a technique for solving this problem, in which a throttle valve has an elliptical shape such that a minor axis thereof in the axial direction of the throttle shaft is smaller than an inner diameter of the suction passage. Another type throttle valve has a substantially elliptical shape having opposite strightly chamfered portions in the vicinity of the throttle shaft, so as to prevent the scuffing or biting of the throttle valve in the vicinity of the throttle shaft.
In the first type throttle valve as mentioned above, there are disadvantageously defined arcuate spaces between the outer periphery of the throttle valve and the inner wall of the suction passage since the elliptical throttle valve is closed in the suction passage having a circular cross section. As a result, leakage of suction air around the throttle valve upon full closing thereof cannot be suppressed. In another respect, if the elliptical throttle valve is deformed by heat into a substantially circular shape, it will scuff the inner wall of the suction passage in the vicinity of the throttle shaft. Further, in mounting the elliptical throttle valve into the suction passage having a circular cross section, the outer periphery of the throttle valve contacts the inner wall only at two points, causing a difficulty of accurate positioning of the throttle valve with respect to the inner wall.
In the second type throttle valve as mentioned above, the straight chamfered portion does not gradually continue from the curved outer periphery of the throttle valve, and there tends to generate burr at the border of the chamfered portion and the curved outer periphery of the throttle valve upon formation of the chamfered portion. This burr causes the scuffing or biting to the inner wall of the suction passage.
In relation to the second aspect of the present invention, a throttle shaft in a conventional throttle body for mounting a throttle valve extends at its one end portion out of a throttle housing defining a suction passage therein, and an arm member is mounted on the extended portion of the throttle shaft. The arm member is provided with adjust screws abuttable against a stopper fixed to the throttle housing. Alternatively, the throttle housing is provided with the adjust screws abuttable against the stopper formed at the arm member. Thus, a rotational angle range of the throttle valve is restricted. Such a structure wherein the adjust screws are located outside the throttle housing is disclosed in Japanese Utility Model Publication No. 51-23783, for example.
In the conventional structure as mentioned above, if the one end portion of the throttle shaft is exposed outside the throttle housing, there will be generated no problem. However, if the one end portion of the throttle shaft is not exposed outside the throttle housing, e.g., in the case that the throttle shaft is provided at its both end portions with a throttle sensor and a valve driving motor, a space cannot be defined for mounting the arm member and locating the adjust screws at the arm member or the throttle housing. Accordingly, it is difficult to construct the afore-mentioned structure. If the afore-mentioned structure is applied to the latter case, there is generated a problem that a foreign matter such as water or dust enters the throttle sensor and the driving motor.
In relation to the third aspect of the present invention, a known drainage structure for the motor is disclosed in Japanese Patent Laid-Open Publication No. 61-121738, for example. The conventional drainage structure includes a drain hole formed through a motor frame and a drain tube connected through a connecting member to the drain hole, so as to prevent entry of water into the motor and also expel the water having entered the inside of the motor to the outside.
In the above drainage structure, when the drain hole having a small cross section is employed, the entry of water may be effectively suppressed, but once the water enters the inside of the motor, it is hard to expel. In contrast, when the drain tube having a large cross section is employed, the water having entered the inside of the motor may be effectively expelled, but the water is easy to enter. Thus, it is hard to satisfy both water resistance and drainage performance in the conventional drainage structure.
Further, in order to promote the drainage performance, a vent hole is generally formed at an upper position of the frame. However, there is a possibility that water will enter the inside of the motor from the vent hole.
Moreover, as the above drainage structure includes the independent drainage parts such as the connecting member and the drain tube, there is also a possibility of these parts being released or damaged because of aged deterioration or external force, causing a reduction in water resistance and drainage performance.
Although a complete sealing structure of the motor may be replaced by the drainage structure, the sealing structure is complicated to cause an increase in cost. Further, in the event that the sealing structure is damaged to allow the entry of water into the motor, the water remains still in the motor to cause a reduction in motor function.
In relation to the fourth aspect of the present invention, a conventional throttle shaft supporting structure is shown in FIG. 23. As shown in FIG. 23, a throttle shaft 412 is fixed to a throttle shaft 414, and the throttle shaft 414 is axially movably supported to a throttle housing 410.
Such an axial movement of the throttle shaft is prevented by a technique disclosed in Japanese Utility Model Laid-Open Publication No. 50-141015, for example. In one example of the technique, ball bearings are press-fitted to the throttle shaft, and dust covers are provided on the outer side of the ball bearings. The dust covers are biased by springs. In another example of the technique, a ball bearing is press-fitted to one end portion of the throttle shaft, and an outer ring of the ball bearing is fixed to the throttle housing by a fixing plug.
Although the above technique can prevent the axial movement of the throttle shaft to some extent, there remains a clearance in the ball bearing. Generally in a ball bearing, an axial clearance is remarkably larger than a radial clearance. Therefore, if resonance of a throttle rotating member due to vibration of an internal combustion engine is generated in the axial direction of the throttle shaft, a rolling surface of the ball bearing is greatly damaged to cause a trouble in operation of the throttle valve.